1. Technical Field
The present invention relates to an audio device and in particular, to a mute function.
2. Related Art
Conventionally, audio devices provided with a headphone output are designed to activate a mute function at the time of power ON/OFF so as not to output a click noise. Further, another function is also suggested to limit an output level so as not to provide an excessive volume output when a headphone plug is inserted into a jack.
JP 11-136789 A describes that an audio output is automatically set to mute or low level in response to pulling out of a headphone plug. The volume is automatically set to zero when a headphone plug is pulled out. The volume should be manually adjusted from the volume zero, when a headphone plug is inserted.
JP 2002-010389 A describes that an audio level is automatically set to mute in response to pulling out of a headphone plug, and then the audio level is automatically returned to a normal level. After the audio level is set to mute, the mute position is maintained until a user adjusts a volume setting.
It should be noted that depending on an impedance or efficiency of respective headphones, actual output levels to the same source output may differ significantly among headphones. Therefore, when headphones are changed with a volume setting left at a high output level, there is a risk that an output will be set at an excessive volume. With JP 11-136789 A, it is possible to prevent an excessive volume by automatically setting an electrical volume to zero (by electrically setting a signal output level to zero) at the time of pulling out of a headphone plug. However, a problem still remains for analog volume. Further, because JP 11-136789 A nowhere provides a specific description about a mute control at the time of power ON/OFF, an excessive volume output is still possible when the power supply is turned from OFF to ON with a headphone plug inserted, depending on a volume setting level.
On the other hand, in JP 2002-010389 A, because a mute mode is maintained until a volume setting is adjusted, there is a problem that an audio output cannot be confirmed until the volume setting is completed. Further, there is another problem that, if a volume setting is erroneously adjusted, an output may be made at an excessive volume when the mute mode is canceled.
The above described problems may occur not only when changing headphones but also when changing an input source.